Antennas are often mounted on the external surfaces of ground vehicles and aircraft. In such situations, it is often desirable for the antenna structure to have the lowest aspect possible. By “aspect” is meant the ratio of height, i.e. extent perpendicular to the mounting surface, to lateral extent, i.e., extent parallel to the mounting surface. For example, a small aspect may be desirable to minimize aerodynamic drag, to reduce visual signature, to improve aesthetic appearance, or for other reasons. In some cases, it may be desirable to conform the antenna to the shape of the mounting surface. The smaller the aspect, the more completely such a goal may be achieved.
However, reducing the antenna aspect may also entail reducing the performance of the antenna. For example, many applications require an antenna having a radiation pattern (in transmission) or sensitivity pattern (in reception) characteristic of an antenna that is electrically polarized perpendicular to the mounting surface. In order to be able to radiate and/or to receive energy polarized along the perpendicular direction, an electrically polarized antenna must extend for at least some height above the mounting surface. Reducing the height will typically reduce the bandwidth and/or the efficiency of the antenna.
Accordingly, there is a need for antennas having very small aspects, but that nevertheless have good performance characteristics such as bandwidth and efficiency. In particular, there is a need for antennas having the aforesaid properties, and further exhibiting radiation or sensitivity patterns characteristic of an antenna that is electrically polarized perpendicular to the mounting surface.